The overall objectives of this project are to investigate the regulation of phospholipid synthesis during functional development of the liver and lung. Emphasis is placed on the biosynthesis of dipalmitoylphosphatidylcholine in lung and the regulation of its formation and secretion as part of lung surfactant. The metabolic pathways are studied by determining the incorporation or radioactive compounds into specific phospholipids and their precursors. The activity and properties enzymes in the biosynthetic pathway are determined during developmental changes in the biosynthetic capabilities. A correlation between the activity and properties of enzymes with the total biosynthetic activity is analyzed in terms of developmental mechanisms for the coordination between tissue function and biochemical properties.